For my new old hobby (Ham Radio) I recently dug out my old 2metre Rig (FDK Multi 750E), and immediately found that it had died, the old historic problem of no TX until I opened it up, then working OK for several weeks even though nothing was touched.. was now no TX or RX either.

I managed to pin both problems down to the grounding of the PCBs via the mounting screws and metal pillars (especially on the PLL PCB) and those were soon solved.

Then having run for 10 mins it started like a steam train... chuff................... chuff..............chuff........chuff... chuff..chuff.chuff.chuff.. and the signal disappeared in between the chuffs as the Phase Locked Loop went unstable.Switching off for a while then back on, it would work for just a minute or so before chuffing off again..

This problem has now also been pinned down to the PLL PCB, where there is a great big blob of something, obviously used to restrict any movement in a very sensitive part of the circuit.Parts of this beige coloured something had turned a dark crispy brown and picking this off the coil former (L7) has given me several days of good working, but it is starting again.. I'm convinced that this 40 year old snot has now gone funny, I've heard of this problem but it's the first time I met it in the flesh.

It looks a bit like expanding foam and is almost solid but just gives a little under the point of a Jewellers driver.. What are your thoughts or tested methods for removing this sorta stuff?I also expect that it is a necessary evil on that part of the circuit so what can then be used to replace it?

I can only recall this stuff being used in VCRs (Sharp, in particular) and it was there, as you surmise, to keep components securely fixed in sensitive circuits where any movement would upset the balance of the circuit.

As to getting it off - I don't think we were ever meant to! It's set like concrete and is near impossible to shift without doing damage.. To me, it looks like the same stuff that disc ceramic caps are dipped in, just as hard, and just as brittle.. I can remember trying methylated spirit to no effect, and similarly, lighter fluid ("Zippo" or "Ronsonol") doesn't affect it.

While there have been problems with Japanese ham kit of this era caused by this sort of gunge, these FDK rigs are notorious for bad solder joints as well as the earthing issues you have identified. I had squelch problems and other strangeness with my 750XX which I cured by going over the pcbs and reflowing just about everything.

Yes, I had also come across and resoldered some nicely circled joints..

With the lack of any serious RF test equipment here or at work, I find that.. when it is working, putting digits anywhere near that gunge triggers the steam engine until removed then it settles again.

Then when it is chuffin chuffing, touching the RX output with a grounded finger kills the chuff and it works fine.So loading the circuit stabilises it, I have considered leaving a high value resistor on there.. but I'd rather cure the actual problem.

Hi Wolfie,If that gunge is similar to say Evostik contact adhesive or a similar type of glue, then I have had some success at removing it in the past by using freezer spray, freezing it makes it brittle and it can be sort of chipped off in small chunks.

As to how you would actually get it of the individual components I couldn't say, because I just replaced standard parts with new if they were badly affected, I realise that might be either very difficult or even impossible in your case.

It does go slightly conductive with age and can actually rot off component legs.

I have the user manual which is more of a service manual than anything, in those days Hams were expected to have the nouse to repair their kit, it includes full circuit diagrams, block diagram, PLL Circuit diagram, layouts etc, but if the actual service manual has more information I would be very grateful of a copy please Niall?

I do like the sound of the Freezer idea, I am going to try the hot air method later in case it softens when warm.

I think most of the components underneath will be standard passives which I can replace. The Semiconductors, I can possibly rescue, but being the most sensitive part of the circuit, making it work again might be the hard bit if I simply shove in a new set of bits.

I'll start small and ramp up my efforts until it's reluctance to move is exceeded, concentrating around the coil first since this is probably where it has most effect.

I managed to chip at least one of the caps probably far enough to require replacement, but otherwise, the hot gun softened the stuff enough to get some purchase then the thin layers peeled away, there are a couple of gouge marks in things but otherwise, I'm pleased with the result.. Maybe not so pleased later when I come to plug it in of course..

This reminds me of the FM section of a lot of AM/FM radios or Japanese/Far Eastern origin where the RF coils were all air cored and mounted on the PCB, alignment being by stretching/compressing individual coils as required.

They used this technique to, presumably, prevent feedback from the speaker vibrating the coils but they used something far simpler in the main - candle wax!

Might be worth considering if you need to replace this acoustic damping in your Transceiver ...

Wolfie wrote:I have the user manual which is more of a service manual than anything, in those days Hams were expected to have the nouse to repair their kit, it includes full circuit diagrams, block diagram, PLL Circuit diagram, layouts etc, but if the actual service manual has more information I would be very grateful of a copy please Niall?

PM sent.

Regarding a replacement for the gunge, hot glue apparently has pretty good RF properties although the "hot" bit might be an issue for some components.

Looking at that sub-PCB it might be an idea to replace the electrolytics. That's the first thing I do when confronted by a delinquent PLL, often results in an immediate repair. When I need to hold components in place or for acoustic damping I always use paraffin wax - good electrical properties and very easy to remove using a warm (thermostatic) iron.

I already changed three Electrolytics to try remove some PLL whine in the Audio background, the ones that came out were fine and the new ones didn't make a blind bit of difference.. so I might belay blitzing them for now.

The Whine has diminished anyway with the removal of the gunge.. Yes, surprise surprise it works, chipped cap and all..

It has been on for about an hour now, I can stick my fat finger in that area and it doesn't give a chuff, I can also breathe heavily on it which previous killed it stone dead for a prolonged period, so long in fact that it was switched off before it came back.Now it doesn't flinch.

So far then it is looking like a fix, thanks for all your input and I'll let you know any developments.

I recall having similar problems in a Sharp VCR that gave strange colour effects. There was a solid black goo all over the chroma chip and surrounding components and after several hours of head-scratching I came to the conclusion that this goo was the cause of all the problems. I also used a hot-melt gun to soften it all but I also had to remove the chroma chip to remove the crud underneath is (all 80 pins of it)! However once everything was back together, it all worked without any further chroma problems.

So far then it is looking like a fix, thanks for all your input and I'll let you know any developments.

Hi Wolfie,

If I may, I'd suggest bees wax, it has far better adhesion than candle wax/paraffin wax.. Also from memory, bees wax was used to good effect in many small transistor radio applications during the 60's and 70's, and definitely easier to shift than that acrylic, or ceramic, or whatever it is "concrete" that you've just chiselled off.

TBH, I thought Beeswax would be softer then candle wax but I'd never considered the difference for this sort of use anyway..

Just at the moment, the PLL side seems to be working OK and the whine has gone completely now so I'll only think about adding some if/when there is a problem associated to that, it is liable to just sit on my desk and not go mobile so should do OK.

I had my first "sched'" using it yesterday evening with a friend about 35miles P2P, and discovered that it is only putting out about half the power it should and the modulation level is low, silly little things that shouldn't take too much sorting out. we also proved that my little Baofeng is deaf as a post compared to two other rigs.

But thanks to Niall and his Information/Manual, today I have managed to acsertain the the PowerTransistor has gone... even though it still puts out 5W (should be 10W). Luckily Argos do them.. (click and collect)

Actually there is a local Radio Rally tomorrow, I might just drop lucky you never know!

Finningley DARS Rally at Sandtoft (M180).. Next to the Trolleybus Museum.. 24th July 2016...

Wish I was close enough to go to that, sounds like a good one. There's a fair chance of picking up 750 bits as quite a few get broken for spares because of the reliability issues. Mine was missing a knob and I got a complete set plus top and bottom case sections and side rails from Ebay a while ago. The A/E models are more common than the XX. I'm going to a couple of small local rallies at the beginning of August, will keep an eye out.

That's the first radio rally we've ever been to but talk about overload, you just didn't know where to look next there was that much "stuff" piled everywhere. A very enjoyable few hours of rummaging and learning too from lots of friendly folk.

I think the next radio rally in this part of the world is on September 18th, Great Northern Hamfest at Barnsley.

That is one of the highlights of a good radio rally - start a conversation with a stallholder about some obscure "thing" and before you know it there is a lively group discussing what it is, what could be done with it, "I had one of those" etc. Of course the upshot is that you eagerly hand over the meagre sum requested and lug the beast home then realise "I don't actually need one of these!" One of these days I will take a rally table and try to sell on various things I have acquired in this way - which is of course what everyone else is doing!

Blend petroleum jelly (Vaseline) and melted candle wax to get the softness you want. It's the same kind of stuff.It's also how the coating for waxies was made. The actual internal material the paper was soaked in varied depending on if hermetic sealed, card or moulded. But supposedly paraffin and petroleum jelly typical.

A piece of sponge in coil and then paraffin wax (candle) to hold in place is common.

There are lower melt point glue sticks. I've not tried them for coils as candle wax (paraffin wax) is easier to remove.

I put cheap stiffer petroleum jelly on IF cores etc to keep them in place, as it's still adjustable.

Thanks for the pointer to those manuals Niall, would yer believe I almost forgot and logged in with less than a minute before the hammer went down... it wasn't a contest so my first bid won them..

Meantime, my OP transistor arrived today, the silver connections were very tarnished but succumbed to the wire pencil, I was amazed how easy it was to replace, then I could set the Idle Current properly.

Then I had less TX power than before!

During my earlier attention I had turned down the OP Power adjustment since it seemed to make little difference from 1/3 of the pot, now I had around 7/8W.

The merest adjustment of the trimmers and it peaked exactly on 10W .. Yay!

I was hoping to do a quick test with my friend who I worked last weekend, but I daresay he's up to his neck in suitcases at the moment.

The PLL (remember, where this started!) has ben absolutely rock steady, the PLL whine in the background has gone completely and even tapping the PCB makes no difference.

So once again it looks like a good repair, until the next problem rears it's ugly head I suppose..

I am amazed at just how many repeaters are onthe air now, some channels have two, separated only by CTSS and of course foreigners on them via DStar or summink! I've heard both Australian and South African Amateurs on EE recently.

Frankly I 'm more surprised that I can get on there from 30odd miles..

There's been a bit of a lift on 2M quite often recently which might account for your co channel repeaters - the last time I was up high with a 2M rig there was a repeater which isn't normally audible from there.

Dstar is digital and just sounds like noise on an analogue rig. The foreign stations would be using Echolink. The repeaters around here theoretically have Echolink but as far as I can tell it's never switched on. We have this little repeater abuse problem the rest of the world doesn't need to hear...

You might want to build a CTCSS board for the 750 for repeater working, don't know how many of your local boxes support toneburst. All my locals do, in fact one of them doesn't have CTCSS; I had to build a toneburst for the Philips FM1000 in the truck which as an ex PMR rig only has CTCSS.

Echolink, I knew it would be something I had no clue about, I have heard the digital racket on repeaters.

I was holding off getting a CTCSS PCB until I knew I had a working rig, but ordered one earlier.

Quite happy with the old rig again, the original problem of intermittent TX had bugged me for some years and I had tackled it several times only to find that it suddenly worked without much input from me and continued to work sometimes for weeks (or often just until the lid was screwed back on)..

Next, I'll go get the Microwave modules transverter and see what hair I can tear out getting that working.